1.Field of the Invention
The present invention relates to an assembly composed of metal leads and a film carrier for use to establish electrical connections between a semiconductor chip and another electric element, an assembly composed of a film carrier and a semiconductor chip, a method of manufacturing the same, a semiconductor device using the assembly composed of the metal leads and the film carrier and a method of manufacturing the same.
2.Description of the Prior Art
Electronic equipment ranging from a handy calculator to a large-scale computer developed recently uses a semiconductor chip employing tape-carrier joining for improving the performance and miniaturization. A schematic structure of tape-carrier joining for use in the foregoing semiconductor device is shown in FIG. 13.
Referring to FIG. 13, a semiconductor chip 101 is connected to a plurality of fine metal leads 103 disposed on a polyimide film carrier 104. The method of assembling the semiconductor chip is called a TAB (Tape Automated Bonding) method. Since the TAB assembling method is a method in which mounting of the semiconductor chip 101 on the tape carrier 104 and joining (inner-lead-bonding) of the metal leads 103 are performed completely automatically, this method exhibits an excellent mass-productivity. The metal leads 103, the inner leads of which have been bonded, and which are placed on the film carrier 104, are cut to have predetermined lengths so that outer leads are formed. Then, the outer leads are subjected to a forming process so as to be adaptable to the state where the semiconductor chip 101 is assembled. Then, the semiconductor chip 101 is, as shown in FIGS. 14A and 14B, mounted on a wiring board 112, and the outer leads are connected (outer-lead-bonding). FIG. 14A shows an ordinary example of an assembled structure in which the reverse side of the semiconductor chip 101 is die-bonded to electrodes 111 of the substrate 112. If heat radiation from the reverse side of the semiconductor chip 101 must be enhanced, a structure as shown in FIG. 14B is employed in which the semiconductor chip 101 is bonded in a face-down manner. In the foregoing assembling methods, the facility of putting together the fine metal leads 103 on the semiconductor chip 101 and the wiring board 112 is improved by, as shown in FIG. 13, enlarging the pitch of the metal leads 103 in the periphery of a device-hole 106 to about three to five times the pitch of the metal leads 103 in the portions in which the connections between the semiconductor chip 101 and the metal leads 103 are established.
An increase in the number of pins resulted from the fact that the semiconductor chip has been highly integrated arises trends that the metal leads on the tape-carrier are fined and that the pitch of the metal leads is made narrow. Therefore, a method has been employed in which the metal leads on a single film are fined, the metal leads are disposed in a multi-layer and the tape-carriers are stacked up so that the number of the bonding leads is increased.
Technologies relating to a semiconductor device of the foregoing type have been disclosed in, for example, Japanese Patent Unexamination Pubication No. 63-62335, Japanese Patent Unexamination Pubication No. 63-164229, Japanese Patent Unexamination Pubication No. 64-19737 and Japanese Patent Unexamination Pubication No. 1-106438.
The foregoing conventional technologies have not been made to satisfactorily form electrodes-required to connect tape-carriers which have been previously stacked up on a semiconductor chip. That is, the tips of groups of metal leads projecting from stacked film carriers form steps that correspond to the number of the stacked layers. In order to perform a bonding uniformly, the heights of the electrodes on the semiconductor chip must be the same as the heights of the metal leads. It has been very difficult to simultaneously form electrodes having different heights on a single semiconductor chip. If the film carrier and the metal leads are thinned to reduce the vertical level difference of the electrodes, the metal leads can easily be etched and appreciation of pins by narrowing the lead pitch can be realized. However, there arises a problem that the metal leads of this type cannot be adapted to assembling of a semiconductor chip in which signals must be transmitted at a high speed. The reason for this is that parasitic capacitance, such as the resistance or the self-inductance or the like of the lead is increased due to narrowing of the widths of the leads caused by the reduction in the lead pitch and due to the reduction in the lead thickness, causing the signal transmission speed to be lowered and crosstalk-noise to be increased.
In the conventional TAB assembling method, a semiconductor chip is bonded on to a tape-carrier and, then, the outer leads are cut and formed into predetermined shapes. Then, the semiconductor chip is mounted on a printed-wiring-board or a ceramic-wiring-substrate. Therefore, the appreciation of pins of the tape carrier and fining of the leads raise problems that adjustment of the positions of the leads is difficult at the time of assembling the substrate on the tape carrier and the bonding process cannot easily be performed. The problems are due to the fact that fining of the leads causes the mechanical strength of the leads to be weakened and, accordingly, the leads are easily deformed even if a small external force is applied. That is, the state of the conventional TAB assembling method where the tips of the cut leads project from the tape carrier causes a bend of a part of the leads and local pitch deviation to take place during the process of forming the leads, the process of adjusting the position of the substrate and the bonding process, resulting in difficulty to handle the elements at the time of assembling the elements.
As described above, the process of assembling a highly integrated and high-speed-operative semiconductor chip on a tape carrier must be performed by selecting the shapes of the leads and maintaining the assembling facility such that the appreciation of pins of the metal leads is realized and the high-speed operation of the device is maintained.